1. Field of the Invention
The present invention relates to wireless communication systems. More particularly, the present invention relates to a method and a system for implementing mobile relay.
2. Description of the Related Art
A Long Term Evolution-Advanced (LTE-A) system aims at implementing mobility which supports a mobile user moving at a high speed of 350 km/h. High speed movements generate high Doppler shifts, which result in a low data transmission rate of users in high speed movements. In addition, due to the high speed movements, a user needs to perform handover frequently between cells, which is power-consuming. Therefore, optimization of the LTE-A system should be carried out in physical layer and upper layers. High speed movements have been featured in most important scenarios in which mobile communications networks are adopted, and design of the network structure has drawn lots of attention.
In high speed trains, user actions in a wireless network such as handovers and cell reselections occur frequently, and there are bursts in usage of wireless network resources, such as frequent inter-cell handover and reselection in a short period, and the like. High speed movements make a user stay in a cell for a very short time. Consequently, delays in signaling and services may have significant impact on mobility performance of the user in the wireless network. Vehicles in high speed movements usually suffer from large penetration loss, which places high requirements on coverage continuity of the wireless network and power consumption of terminals. In high speed movement scenarios, the Doppler Effect plays an important role, and Doppler shifts have significant impact on service quality. In addition, as wireless communication systems become more prevalent, terminal users may generate high demands for data services. Therefore, current frequency resources cannot satisfy service requirements of terminal users in high speed movements.
At present, according to the related art, one of the solutions to address the demands in high speed movement scenarios is mobile relay stations. 3rd Generation Partnership Project (3GPP) Release 10 (Rel-10) only supports fixed relay, and a relay station can only work on a single frequency with one antenna. In Release 11 (Rel-11), it is being discussed to introduce mobile relay for supporting high speed mobility, and carrier aggregation and multi-antenna are allowed to be used to enhance capacity and performances of mobile relay. At present, the capacity of backhaul links and access links of a relay system has become a bottleneck which impacts user data rate in high speed movements. An enhanced multiple antenna transmission technique is one solution for increasing the capacity of a relay system, but the Doppler shifts have influence on link quality. Another solution for increasing the capacity of a relay system is using carrier aggregation, but spectrum resources that can be used for mobile communication are rare according to the related art.
Therefore a need exists for addressing the bottleneck in backhaul link capacity and access link capacity of a relay system in high speed movement scenarios. For example, a need exists for a system and method for implementing mobile relay.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.